知识点

1. 贪心

题目描述

思路讲解

代码展示

#include <iostream>
#include <algorithm>using namespace std;const int N = 100010;int n;struct Range {int l, r;bool operator < (const Range &W) const {return l < W.l;}
} range[N];int main() {int st, ed;scanf("%d%d", &st, &ed);scanf("%d", &n);for (int i = 0; i < n; i++) {int l, r;scanf("%d%d", &l, &r);range[i] = {l, r};}sort(range, range + n);int res = 0;bool success = false;for (int i = 0; i < n; i++) {int j = i, r = -2e9;while (j < n && range[j].l <= st) {r = max(r, range[j].r);j++;}if (r < st) {res = -1;break;}res++;if (r >= ed) {success = true;break;}st = r;i = j - 1;}if (!success) res = -1;printf("%d\n", res);return 0;
}